I built a simple project with my son. It's sort of a nightlight where four led's are connected to the Arduino via a breadboard and there's a button attached to it. He pushes the button and the lights go on and again and the lights go off. I figured the LED didn't use much power so it could be run off of a 9 volt battery for a good amount of time.

We connected a 9 volt battery to the power connector. It worked great as his first stand-alone device. He didn't use it yet, but overnight the battery drained, even though the button wasn't pressed and the LED's weren't on. Any ideas why? I noticed there's a little light lit on the board even when the button isn't pressed. Could that tiny light be draining the battery?

Cool dad to work with your son on projects. I recommend using this for further learning. The first go round works, but has some problems.

The 9V does not have much capacity and the project uses power even when on. Brain storm on how to improve that.

Since going to a simple resistor, switch, and battery would sort of be going backwards how about figuring a way to do the same thing with component or more simple logic chip. What you have is a flip flop circuit.

There are ways to put the Arduino microcontroller into sleep mode, but most Arduino boards also have a usb->serial chip which uses 15mA too. For low power standby you need a standalone board without the USB->serial chip, and to use one of the libraries that allows putting the microcontroller into low-power sleep modes.

I built a simple project with my son. It's sort of a nightlight where four led's are connected to the Arduino via a breadboard and there's a button attached to it. He pushes the button and the lights go on and again and the lights go off. I figured the LED didn't use much power so it could be run off of a 9 volt battery for a good amount of time.

We connected a 9 volt battery to the power connector. It worked great as his first stand-alone device. He didn't use it yet, but overnight the battery drained, even though the button wasn't pressed and the LED's weren't on. Any ideas why? I noticed there's a little light lit on the board even when the button isn't pressed. Could that tiny light be draining the battery?

Having prototyped the system on an Arduino, I would build a minimal atmega328p design on a piece of stripboard, and program it to be in sleep mode most of the time. If you want to stick with the 9V battery as the power supply, use a micropower regulator to provide the 5V supply, such as the MCP1702-5002E.

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.